1) Create a Blueprint asset class derived from PrimaryDataAsset.
2) Create an asset of the class from step 1 via Miscellaneous → Data Asset.
3) Create a Blueprint structure and added a property with the type from step 1, assigning a default value from step 2.
4) Create a BehaviourTreeTask class and add a field with the type of the structure from step 3.
5) Create a BehaviourTree and add the task from step 4.
6) Restart the project.
7) Open the behaviour tree & the output log.
8) Observe the error/warnings provided in the callstack section of this report.
Note that opening the user defined structure first will not cause any error/warnings to occur.
User has provided a minimal repro project.
LogProperty: Error: FStructProperty::Serialize Loading: Property 'StructProperty /Game/BTT_BTTask.BTT_BTTask_C:AbilityData'. Unknown structure.
LogClass: Warning: Struct Property AbilityData has a struct type mismatch (tag STRUCT_REINST_S_UserDefinedStructure_4(/Engine/Transient) != prop FallbackStruct(/Script/CoreUObject)) in package: /Game/BTT_BTTask. If that struct got renamed, add an entry to ActiveStructRedirects.
LogProperty: Warning: Serialized BlueprintGeneratedClass /Game/DA_AssetClass.DA_AssetClass_C for a property of LinkerPlaceholderClass /Game/S_UserDefinedStructure.PLACEHOLDER-CLASS__DA_AssetClass_C_0. Reference will be nulled.
ReferencingObject = UserDefinedStruct /Game/S_UserDefinedStructure.S_UserDefinedStructure
Property = ObjectProperty /Game/S_UserDefinedStructure.S_UserDefinedStructure:PrimaryAsset_10_620218C04F61459D99F1D0A6AB388374
Item = DA_AssetClass_C /Game/DA_Asset.DA_Asset
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-368838 in the post.
| 1 |
| Component | UE - Framework - Blueprint |
|---|---|
| Affects Versions | 5.7 |
| Created | Mar 6, 2026 |
|---|---|
| Updated | May 1, 2026 |